This article investigates the legitimising role of hydropower dams in authoritarian regimes, with a focus on Cambodia and Laos. Drawing on fieldwork observations conducted between 2018 and 2023, alongside secondary sources, it adopts a content analysis approach to explore how dam-related legitimacy aligns with broader typologies of legitimacy. Although both regimes are authoritarian and utilise hydropower as a socio-economic and symbolic tool to reinforce their authority, they do so in distinct ways. The Laotian government primarily mobilises hydropower to assert performance and identity legitimacy, emphasising developmental success and national identity. In contrast, the Cambodian regime must negotiate between performance and procedural legitimacy, which shapes its hydropower discourse differently. These variations reflect how authoritarian legitimacy is not uniform but contextually shaped by political institutions, economic constraints, and available resources. The study contributes to the literature on authoritarian governance by illustrating how infrastructure projects become instruments of regime legitimation across political landscapes.